THEORY OF THE EARTH. 185 



this inquiry, to observe the heliacal risings and 

 settings of the stars. We know that they chose 

 particularly the heliacal rising of Sirius, at first, 

 doubtless, on account of the beauty of the star ; 

 and, especially, because, in those ancient times, 

 this rising of Sirius being nearly coincident with 

 the solstice, and indicative of the inundation, was 

 to them the most important phenomenon of this 

 kind. Hence it was that Sirius, under the name 

 of Sothis, occupied so conspicuous a place in their 

 mythology, and in their religious ceremonies. 

 Supposing, therefore, that the return of the he- 

 liacal rising of Sirius and the tropical year were 

 of the same duration, and believing, at length, 

 that this duration was 365 days and a quarter, 

 they would imagine a period after which the tro- 

 pical year and the old year, the sacred year of 

 365 days only, would return to the same day ; a 

 period which, according to these incorrect data, 

 was necessarily 1461 sacred years, and 1460 of 

 those improved years to which they gave the 

 name of years of Sirius. 



They took for the point of departure of this 

 period, which they named the Sothiac or great 

 year, a civil year, the first day of which was, or 

 had been, also that of a heliacal rising of Sirius ; 

 and it is known, from the positive testimony of 

 Censorinus, that one of these great years had 



